Plausibility of ultraviolet burst generation in the low solar chromosphere

Abstract

Ultraviolet (UV) bursts and Ellerman bombs (EBs) are small-scale magnetic reconnection events taking place in the highly stratified, low solar atmosphere. It is still not clear whether UV bursts have to be generated at a higher atmospheric layer than EBs or whether both UV bursts and EBs can occur in the low chromosphere. We numerically studied the low $\beta$ magnetic reconnection process around the solar temperature minimum region (TMR). The time-dependent ionization degrees of hydrogen and helium are included in the MHD code, which lead to a more realistic magnetic diffusion caused by electron-neutral collision and ambipolar diffusion. A more realistic radiative cooling model from Carlsson & Leenaarts 2012 is included in the simulations. Our results in high resolution indicate that the plasmas in the reconnection region are heated up to more than $20,000$ K if the reconnecting magnetic field is as strong as $500$ G, which suggests that UV bursts can be generated in the dense low chromosphere. The dominant mechanism for producing the UV burst in the low chromosphere is heating, as a result of the local compression in the reconnection process. The thermal energy occurring in the reconnection region rapidly increases after the turbulent reconnection mediated by plasmoids is invoked. The average power density of the generated thermal energy in the reconnection region can reach over $1000$ erg cm${}^{-3}$ s${}^{-1}$, which is comparable to the average power density accounting for a UV burst. With the strength of the reconnecting magnetic field exceeding $900$ G, the width of the synthesized Si IV 1394 A line profile with multiple peaks can reach up to $100$ km s${}^{-1}$, which is consistent with observations.

12 pages, 10 figures

References in corpus (14)

• Hot Explosions in the Cool Atmosphere of the Sun
• CHIANTI - an atomic database for emission lines - Paper XV: Version 9, improvements for the X-ray satellite lines
• Critical Science Plan for the Daniel K. Inouye Solar Telescope (DKIST)
• Ellerman bombs and UV bursts: transient events in chromospheric current sheets
• Heating mechanisms in the low solar atmosphere through magnetic reconnection in current sheets
• Magnetic reconnection in strongly magnetized regions of the low solar chromosphere
• Coronal microjets in quiet-Sun regions observed with the Extreme Ultraviolet Imager onboard Solar Orbiter
• Flame-like Ellerman Bombs and Their Connection to Solar UV Bursts
• Asymmetric Magnetic Reconnection in Weakly Ionized Chromospheric Plasmas
• The eruption of a small-scale emerging flux rope as the driver of an M-class flare and a coronal mass ejection
• A Magnetic Reconnection model for Hot Explosions in the Cool Atmosphere of the Sun
• Two strong white-light solar flares in AR NOAA 12673 as potential clues for stellar superflares
• Multi thermal atmosphere of a mini solar flare during magnetic reconnection observed with IRIS
• High-resolution Observations of Small-scale Flux Emergence by GST

Cited by in corpus (7)

• A comparative study of resistivity models for simulations of magnetic reconnection in the solar atmosphere
• Small-scale magnetic flux emergence preceding a chain of energetic solar atmospheric events
• A comparative study of resistivity models for simulations of magnetic reconnection in the solar atmosphere. II. Plasmoid formation
• Extreme-ultraviolet (EUV) observables of simulated plasmoid-mediated reconnection in the solar corona
• Theoretical Studies on the Evolution of Solar Filaments in Response to New Emerging Flux
• High $\beta$ magnetic reconnection at different altitudes in the cool low solar atmosphere
• Hard X-rays from the deep solar atmosphere. An unusual UV burst with flare properties